The present invention relates to electrodeless light sources excited by high frequency power and, more specifically, to techniques and apparatus for optimizing the transfer of power from a source to the lamp.
Historically, there have been three methods of exciting discharges with electrodes. The first uses the discharge as a lossy part of either the capacitance or inductance of a tank circuit. A second method is to place the lamp in the path of radiation from a directional antenna. A third method uses a resonant cavity which contains the lamp and a device for matching the cavity impedance to the source and transmission line. Examples of a device according to this third method may be found in "Microwave Discharge Cavities Operating at 2450 MHz" by F. C. Fehsenfeld et al., Review of Scientific Instruments, Volume 36, Number 3, (March, 1965). Another example of a resonant cavity device is described in the U.S. Pat. No. 3,787,705 to Bolin.
All of these methods have disadvantages which limit their use as a possible replacement for the conventional incandescent light bulb. One feature of the electrode-containing source is the capability of brightness selectivity control, such as with a potentiometer. An electrodeless lamp containing a fill material that emits light upon breakdown and excitation may have an impedance in the operating mode having both an imaginary and a real component. Further, each component may vary with the power applied to the lamp. Thus, some technique is desirable to optimize the transfer of power from the source to the lamp when the source-power level is adjustable.